1. Field of the Invention
The present invention relates to a device for displaying a large-sized image, and more particularly, to a display device in which the optical efficiency is enhanced by using a color drum.
2. Description of the Related Art
Recently, a flat panel display that has thin and large-sized screen attainment characteristics attracts public attention, and is anticipated to replace the conventional cathode ray tube (CRT) that has a limitation in the screen size and a large volume. As such a flat panel display, there are a liquid crystal display (LCD), a plasma display panel (PDP), a projector and the like. Among these flat panel displays, the projector that magnifies a small-sized image made by an LCD and projects the magnified image to a large-sized screen through a projection lens stands in the spotlight as a new large-sized screen display.
The projector includes a lamp system for generating light, an optical system for converging the generated light, an image display device for displaying the converged light as colors according to an inputted electric signal, and a projection system for magnifying and projecting the displayed colors. Here, the image display devices are classified into a transmission type image display device for transmitting an incident light according to an inputted electric signal and a reflection type image display device for reflecting the incident light according to the inputted electric signal. The LCD having an advantage of the slimness is mainly used as the image display device.
Recently, as a small-sized image display device is developed, various kinds of projectors are being commercialized. The projectors are generally classified into single panel type using one sheet of image display device, double panel type using two sheets of image display devices and triple panel type using three sheets of image display devices. The single panel type projector that uses one sheet of image display device to display images is currently widely used in aspects of cost and structure.
The single panel type projector can use any one of three ways to express the white color: a first way in which R, G and B color filters are attached to the image display device to express the white color, a second way in which micro lenses are attached to the image display device to split R, G and B color lights in different directions and to express the white color, and a third way in which color wheels are utilized to transmit R, G and B color lights selectively one after another in time order.
FIG. 1 illustrates a conventional projector in which color filters are attached to the image display device and FIG. 2 illustrates a conventional projector in which a micro lens is attached to the image display device.
Referring to FIG. 1, in an image display device 120, R, G and B pixels 122 are linearly arranged and a filter 124 is attached to each pixel 122. Light generated by a lamp system 100 is converged by an optical system 110 and incident into the image display device 120. Here, the image display device 120 expresses the incident light as colors according to inputted electric signals. Accordingly, the converged light is expressed as colors depending on the electric signal inputted to each pixel 122 of the image display device 120, and transmits the filter 124 or is reflected by the filters 124. The transmitted colors are magnified and outputted onto a screen 140 by a projection lens 130.
In such a way, however, since three pixels (R, G, B) express one white light, the total number of pixels on the image display device 120 express the white color of which the resolution is reduced to one third (⅓). Like this, since so large area is required to express one white color, the resolution is lowered. In addition, since the filters 124 attached to the image display device 120 do not have good transmission characteristics, they lower the optical efficiency.
As an alternative proposal, referring to FIG. 2, micro lenses 165 each of which corresponds to three pixels 161, 162 and 163 of R, G and B are arranged on an image display device 160. Separate R, G and B reflection mirrors 152, 154 and 156 are provided between the optical system 110 and the image display device 160 in order to split the light and apply the split lights to the pixels 161, 162 and 163 at specific angles respectively. Accordingly, the light generated by the lamp system 100 passes the optical system 110, is split into color lights by the reflection mirrors 152, 154 and 156, and is then incident into the image display device 160 at different angles depending on the slopes of the reflection mirrors 152, 154 and 156. The image display device 160 receives the lights inputted from the reflection mirrors 152, 154 and 156 through the micro lenses 165 and sends them to corresponding pixels 161, 162 and 163 to express colors according to the inputted electric signal.
However, even in such a way, since three pixels express one white color like the way in which filters are attached to the image display device (shown in FIG. 1), the resolution is lowered.
To solve the lowering problem in the resolution appearing in the ways of FIGS. 1 and 2, a way shown in FIG. 3 has been suggested.
FIG. 3 illustrates a conventional projector using a color wheel.
Referring to FIG. 3, an image display device 180 includes white pixels 182, 183 and 184 arranged to express one white color by one pixel and a color wheel 170 between a lamp system 100 and an optical system 110. The color wheel 170 has R, G and B transmission filters 174a, 174b and 174c arranged on predetermined areas of a rotation disk.
As the light generated by the lamp system 100 is incident into the color wheel 170, the color wheel 170 is rotated by a motor 172 to split the incident light into color lights sequentially and transmit the split color lights to the optical system 110. Then, the optical system 110 converges the split color lights to one white pixel of the image display device 180 to express a white color.
Since the above method can express one white color by one white pixel, the resolution is enhanced by three times compared with the related arts shown in FIGS. 1 and 2 but the brightness is contrary decreased to one third (⅓). This is because the color wheel 170 transmits only the corresponding lights of the respective transmission filter 174a, 174b and 174c and the remaining light is not transmitted but lost to decrease the amount of light so. Accordingly, the light efficiency is decreased.
According to the way described above, the resolution is good but the brightness is bad. To this end, there is being developed a technology which is based on the way shown in FIG. 3 and in which the light reflected from the color wheel and lost is reused to enhance the light efficiency.
FIG. 4 illustrates a conventional projector provided with a road lens.
Referring to FIG. 4, a conventional projector includes a lamp system 210 for generating light, a road lens 220 shaped in a rectangular, for receiving the light generated from the lamp system 210, totally reflecting and outputting the generated light, and totally reflecting and outputting the re-inputted light, a color wheel 230 for selectively transmitting the light outputted from the road lens 220, a converging lens 240 for converging the transmitted light from the color wheel 230, an image display device 250 for expressing the converged light in colors, and a projection lens for magnifying and projecting the colors expressed by the projection lens 260 onto a screen 270.
The lamp system 210 includes a light source 212 for generating the light and an elliptic reflecting mirror 214 for controlling the generated light to be inputted to the road lens 220. Accordingly, all the light generated by the converging lens 210 is incident into the road lens 220.
The road lens 220 includes an inside made of optical glass or optical plastic. Alternatively, the inside of the road lens 220 may be a vacant space. Also, the outer wall of the road lens 220 is coated with a total reflection material. In addition, an opening 224 is formed in an input surface 222 so that the light generated by the lamp 210 can be incident into the inside of the road lens 220. The remaining region 226 except for the opening 224 is coated with a reflection material. Like this, it is desirable that the region 26 is coated with a reflection material such that the light reflected by the color wheel 230 and inputted into the road lens 220 is reflected again and outputted onto the color wheel 230. Accordingly, the road lens 220 receives the light generated by the lamp system 210 through the opening 224, totally reflects it therein and outputs it to the color wheel 230 through an output surface 228.
Although the light generated by the lamp system 210 has a low uniformity in brightness, it is outputted uniformly through the output surface 228 by the total reflection in the inside of the road lens 220. Here, the brightness uniformity is changed depending on the length of the road lens 220 and a kind of the medium.
The light outputted from the road lens 220 passes the color wheel 230 or is reflected by the color wheel 230. At this time, the light reflected by the color wheel 230 is again incident into the road lens 220, is totally reflected inside the road lens 220 and is again outputted to the color wheel 230. Here, the light outputted to the color wheel 230 has a different light path than the light outputted from the road lens 220. This is because the angle of the light reflected by the color wheel 230 and the position of the light reflected totally in the road lens 220 are different from those of the first outputted light. For example, if the first outputted light is inputted to the color wheel 230 via the center of the output surface 228 of the road lens 220, the light reflected by the color wheel 230 can be again inputted to the position other than the center of the output surface 228 of the road lens 220 according to the reflection angle. Also, since the re-inputted lights are reflected totally at different locations inside the road lens 220, the final position of the light outputted to the output surface 228 of the road lens 220 becomes different from the position of the light first outputted to the color wheel 230. Similarly, since the first light outputted to the color wheel 230 is different from the final light outputted to the color wheel 230, each color light can be transmitted.
The color wheel 230 is arranged to face the output surface 228 of the road lens 220 at the same area. The R, G and B transmission filters are formed in a spiral configuration. By forming the transmission filters in a spiral configuration, R, G and B color lights can be outputted through the transmission filters uniformly.
Thus, when the color wheel 230 is comprised of spiral filters, the color lights outputted through the color wheel 230 have curved boundary surfaces 234 and 236.
As shown in FIG. 5, when the color wheel 230 is rotated by a motor 232, R, G and B transmission filters move sequentially to pass the corresponding color lights selectively. After that, if the passed color lights are incident into the image display device 250 through the converging lens 240, color lights having the curved boundary surfaces 234 and 236 appear.
To this end, there is required an algorithm for converting the color lights having the curved boundary surfaces 234 and 236 to a linear type of color lights. However, the algorithm for converting the color lights having the curved boundary surfaces 234 and 236 to a linear type of color lights is very complex, which is problematic.
In the meanwhile, to convert the color lights having the curved boundary surfaces 234 and 236 to a linear type of color lights, it is desirable that the color wheel is made as great as possible. However, the use of the great color wheel causes a problem that the volume of the color wheel increases. Of course, even if the color wheel is made great, the boundary surfaces 234 and 236 are not perfectly converted to a linear arrangement.
Also, as shown in FIG. 6, the flat color wheel 230 of the conventional projector faces the output surface 228 of the road lens 220. To this end, in case the lights outputted through edges of the road lens 220 are reflected by the color wheel 230, the reflected lights are not re-inputted to the road lens but are lost outside the road lens 220. As a result, the loss of the light outputted through edges of the road lens reduces the whole light brightness.
Accordingly, the present invention is directed to an optical system and display device using the same that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a display device in which a cylindrical color drum is used to reduce light loss occurring between a road lens and the color drum as great as possible and thus enhance light efficiency.
Another object of the present invention is to provide a display device in which a rectangular transmission filter is provided on a cylindrical color drum to output a linear boundary surface and thus simplify the signal processing of the display device.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided an optical system. The optical system includes: a road lens for totally reflecting light inputted from an outside, changing a path of the light and outputting the light; a cylindrical color drum having a plurality of cell filters arranged orderly along a circumference thereof to face the path of the light so that the light outputted from the road lens is transmitted selectively; and a converging lens for converging the light transmitted through the color drum.
According to the optical system, the road lens includes: an input surface having an opening for transmitting the light inputted form the outside and a reflection region coated with a reflection material; side portions for totally reflecting the light inputted though the input surface; and an output surface for outputting the total reflected light from one of the side portions. Here, the road lens further includes a reflecting surface slanted by a predetermined angle from the output surface to change the path of the light inputted though the input surface. Also, the output surface includes an opening sized to at least include the plurality of cell filters of the color drum.
The plurality of cell filters of the color drum have surfaces arranged to face the output surface in the form of a curved surface. Alternatively, the plurality of cell filters are arranged in a linear type.
According to the optical system, the road lens includes: a side portion; an input surface formed at a predetermined region of the side portion, the input surface having an opening through which the light inputted from the outside is transmitted and a reflection region, the side portion totally reflecting the light inputted though the input surface; and an output surface for outputting the total reflected light. The road lens further includes a reflecting surface slanted by a predetermined angle from the output surface to change the path of the light inputted through the input surface.
In another aspect of the present invention, there is provided a display device of magnifying and projecting a small-sized image to display a large-sized image, the device includes: a lamp system for generating light and converging the light; an optical system including a road lens for uniformly outputting the light converged by the lamp system, a color drum having a plurality of cell filters arranged orderly along a circumference thereof to face the path of the light outputted from the road lens, and a converging lens for converging the light transmitted through the color drum; an image display device for expressing the light converged by the optical system in colors according to an applied electric signal; and a projecting system for magnifying and projecting the colors expressed by the image display device.
According to the display device, the road lens includes: an input surface to which the light generated by the lamp system is inputted; a side portion for totally reflecting the light inputted through the input surface; an output surface for projecting the light reflected totally by the side portion to the color drum; and a reflecting surface slanted by a predetermined angle from the output surface, for changing a path of the light inputted from the lamp system.
Also, the road lens includes: an input surface to which the light generated by the lamp system is inputted; a reflecting surface slanted by a predetermined angle from the input surface, for changing the path of the light inputted from the lamp system; a side portion for totally reflecting the light the path of which is changed by the reflecting surface, the input surface being formed on a predetermined region of the side portion; and an output surface for outputting the light reflected totally by the side portion to the color drum.
In another aspect of the present invention, there is provided a display device of magnifying and projecting a small-sized image to display a large-sized image. The device includes: a lamp system for generating light and converging the light; a road lens for uniformly and totally reflecting the light converged by the lamp system; a color drum having a plurality of cell filters arranged orderly along a circumference thereof to face the path of the light outputted from the road lens; a converging lens for converging the light transmitted through the color drum; an image display device for expressing the light converged from the optical system in colors according to an electric signal; and a projecting system for magnifying and projecting the colors expressed by the image display device.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.